Various techniques are known in the art for isolating between different signals used in cardiac therapy. For example, U.S. Patent Application Publication 2009/0306641, whose disclosure is incorporated herein by reference, describes an array of notch filters for keeping Radio Frequency (RF) ablation energy from penetrating through a pacing circuit. The array comprises two branches of notch filters with high impedance in the frequency range that is used for ablation: one branch protecting the signal path between the pacing circuit and the catheter tip, and the other protecting the return path. The filters have low impedance at the pacing frequency, thus permitting pacing to proceed simultaneously with ablation.
U.S. Pat. No. 7,894,885, whose disclosure is incorporated herein by reference, describes a method for monitoring an electrocardiogram (ECG) signal of a subject. The method includes digitally sampling an average signal from at least a first ECG electrode, determining an average interference frequency, and digitally sampling and buffering a raw ECG signal from at least a second ECG electrode. The method further includes filtering the raw ECG signal to generate a residual signal, calculating, based on the residual signal, a first amplitude and a first phase shift of a primary interference signal at the average interference frequency and a second amplitude and a second phase shift of one or more harmonic interference signals at respective multiples of the average interference frequency, and digitally subtracting the primary interference signal and the harmonic interference signals from the raw ECG signal so as to generate and output a clean ECG signal.
U.S. Pat. No. 6,647,289, whose disclosure is incorporated herein by reference, describes a cardiorespiratory monitor that generates bioimpedance sensing signals that produce substantially no interference with bioimpedance signals generated by implanted devices. The monitor detects the bioimpedance signal generated by the implanted device. The monitor analyzes this detected signal to generate a bioimpedance sensing signal that will not interfere with the sensed signal. For instance, if the monitor produces a pulsed sensing signal, the pulses are delivered in an interval of the detected signal where no pulses are present. Similarly, if the monitor produces a high frequency AC sensing signal, the zero crossings of the AC sensing signal are positioned during the delivery of a pulse by the implanted device.